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Analyzing Combustion Processes
March 1, 2013   
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Prof. Piotr Wolański, from the Institute of Heat Engineering at the Warsaw University of Technology, talks to Karolina Olszewska.

Between 2008 and 2012, you headed a research team that developed an innovative system for use in the diagnostics of combustion processes. The system is based on the electrical capacitance tomography (ECT) method and helps increase the cost efficiency of power generation equipment and improve the safety of aircraft engines. What inspired you to start working on a project like this?

You could say we took inspiration from everyday life. We wanted to address the increasingly restrictive international regulations on environmental protection, especially cuts in toxic emissions. For years, the science community around the world has been working to upgrade diagnostic methods which help optimize combustion processes. The primary objectives include systems to reduce the formation of toxic compounds, highly efficient systems for catalytic purification of exhaust gases, and the promotion of alternative fuels. Combustion diagnostics is a broad and rapidly developing field of research. Even though there are many available diagnostic systems, the search continues for new and better ones. Back in the 1990s, the Department of Aircraft Engines at the Institute of Heat Engineering joined in the search and we headed a project aimed at finding a way to use electrical capacitance to monitor and produce a visual image of combustion processes.

The project was carried out from 2008 to 2012 and involved many employees from our institute, along with graduate and postgraduate students. What we found particularly enticing about the project was the opportunity to develop one of the world’s first methods to conduct the diagnostics of combustion processes both online and in situ. The Combustion Laboratory at the Institute of Heat Engineering is a leading facility in research on combustion processes. We study industrial burners, piston engines and jet engines and we pass this expertise on to students at the Warsaw University of Technology.

How are combustion processes analyzed?

At present, direct examination of combustion processes usually involves the use of different kinds of probes and sensors, but those fail to provide comprehensive information on the processes that occur inside combustors and burners. This is, for example, the case when the temperature of exhaust gases is monitored. The currently available optical methods for analyzing combustion processes, such as the streak, shadow and interferometric methods, rely on changes in the index of refraction caused by differences in the density of the medium through which light passes. Each of these methods comes with certain limitations. For example, they require high-end endoscopes, which prevents the methods from being used in real-life conditions and radically increases the costs. Such significant drawbacks make it vital to seek new methods. Electrical capacitance tomography ushers in a totally different approach to combustion diagnostics.

How does it work and what is so inventive about it?

The method used in our project hinges on the analysis of changes in the electric field between electrodes, triggered by chemical reactions occurring in the course of combustion. Research shows that electric charges are chiefly carried by positively and negatively charged ions and free electrons which are essentially produced during combustion. A computer uses a special algorithm to collect the results of the measurements and then uses the results to produce an image of the flame on a monitor. Since the images show specific cross-sections of the combustion area, the system not only establishes that a combustion process has occurred, but it also recreates the chemical reactions. This is what makes the method different from commonly used flame sensors.

The chief advantage of the electrical capacitance tomography system is that it is simple and inexpensive, which makes it almost the perfect tool to perform combustion diagnostics. When put to work, it will dramatically improve the cost efficiency of power generation equipment and improve the safety of running aircraft engines. Even a small divergence from the optimal injector performance parameters in such engines can disrupt the combustion process and push the temperature of exhaust gases above the permitted level. The same problem can lead to uneven temperature distribution inside an engine, which could cause the combustor to overheat and damage the entire engine as a result. Once combustion processes are monitored in real time, it will be possible to assess whether injectors and the combustor system are functioning properly, allowing maintenance crews to intervene as soon as the engine starts to malfunction. When used with turbine engines, the system will dramatically improve flight safety.

What is the electrical capacitance tomography system made of?

It consists of three main modules: a computer, a measurement system, and a set of sensors. Each sensor is made up of electrodes mounted symmetrically around the area where the combustion process will take place. Each pair of electrodes serves as an air capacitor. The measurement system is designed to probe how electrical capacity changes between individual electrode pairs. The computer, in turn, serves a double purpose. It oversees the measurement system and uses the obtained results to create tomographic images. It also analyzes the results.

Are systems like this already used in practice?

Electrical capacitance tomography is mainly used to monitor the two-phase flow of oil and natural gas in oil refineries, and it also comes helpful in pneumatic conveyor systems. Research shows that this kind of tomography also enables the imaging of combustion processes. We expect producers of industrial burners to be the main users of our system and we hope the power engineering sector and oil refineries will become interested in it as well. Our system can be adapted for use in existing heating systems.

Producers of aircraft engines could invest in the further development of the project. As part of an offset contract, we have teamed up with Pratt & Whitney Canada, a division of the U.S.-based aircraft engine producer. This has provided us with extra funds for further research on how electrical capacitance tomography can be used to monitor combustion processes in jet engines fitted with annular combustors. In previous years, we also worked with Pratt & Whitney in the United States.

We also conducted research at the training center of the Weishauptcompany, a leading global producer of gas and oil burners and heating systems. The company is interested in incorporating our technology into its heating systems which employ high-power burners.

We continue to look for businesses interested in using electrical capacitance tomography to enhance the performance and quality of their products. Our research findings enable us to offer cutting-edge R&D services meeting top international standards. That, in turn, ensures closer cooperation between the business sector and the research and development sector.

The results of your research will be subject to intellectual property protection, is that correct?

The principle underlying the system’s functioning as such cannot be patented. The measurement methodology applied in the system has been described in a variety of publications, and many different research centers have been using it for more than a decade. But patent protection can be sought for the system’s application in industry, should the know-how be used for a specific purpose.

The Institute of Heat Engineering is the only research center in Poland to be pursuing research of such kind. Various research centers around the world have recently taken an interest in this technology, but since we have studied the applications of electrical capacitance tomography in combustion diagnostics for over a decade, we lead the way in this field internationally.

How much did the project cost?

The National Center for Research and Development provided zl.1 million for the development of the electrical capacitance tomography system. We used the funds to devise a new measurement system, modernize our laboratory and test the ways in which the system could be used to monitor industrial burners and turbojet engines. We built several test stations fitted with industrial burners and a station with a GTD-350 engine combustor. The stations help demonstrate what the system can do and are also used as teaching aids during classes and in research conducted by students working on their engineering and M.Sc. degrees.
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